A battery is a device that converts chemical energy into electrical energy by means of an electrochemical reaction. With the ever-increasing market for portable electronic devices, such as cell-phones, laptop computers, there is also an increased need for improved energy sources. Most of the electronic products today use “state-of-the-art” batteries, and yet the performance of these leaves much to be desired. Another aspect is the environmental threat posed by the heavy metals used in many of today's batteries. As society is becoming more aware of these problems, the desire for environmentally friendly battery components is growing.
Many of the electrical devices that consumers demand are limited by their power source. From electric vehicles to cellular phones, advances in battery technology have not kept pace with the power requirements of electrical devices. Lithium metal batteries have been targeted as the next generation power sources for these devices, since lithium has the most electropositive potential (−3.04 V versus standard hydrogen electrode), lowest equivalent weight (6.94 g/mol), lowest specific gravity (0.53 g/cm3) and highest mass ratio. These properties facilitate the design of storage systems with higher energy density compared with other battery systems.
A battery includes at least three main components: cathode, electrolyte and anode. The cathode is the electrode where a reduction reaction occurs, whereas the anode is the electrode where an oxidation reaction occurs. The electrolyte is an electronic insulator and a good ionic conductor. One of the electrolyte's main functions is to provide a transport medium from one electrode to the other. Although significant progress has been made in the development of batteries, several factors, such as the electrolyte, have limited their commercial use.
Electrolytes should be chemically and electrochemically stable, mechanically strong, safe and inexpensive. Liquid electrolytes facilitate high-ionic mobility. However, due to safety concerns involving leakage and flammability, the use of liquid electrolytes in lithium battery systems has often been deterred. While solid electrolytes, such as ceramic and polymer electrolyte, prevent the formation of vapor-pressure and leakage problems, ionic transport within these materials is often too slow for typical battery applications. Ideally, an electrolyte would have the electrical properties of a liquid and the mechanical properties of a solid. Such an electrolyte would serve both as electrolyte and separator, and would provide the battery with mechanical flexibility, a property unattainable in cells with conventional liquid electrolytes.
Gel electrolytes possess both the cohesive properties of solids and the diffusive transport properties of liquids. This duality enables the gel to find a variety of applications. Gels can be obtained as a result of either a chemical or a physical linking process. The use of substantial amounts of plasticizers in gel electrolyte gave rise to problems such as but not limited to loss of mechanical strength, and exudation of solvent, which subsequently lead to thermal, chemical and electrochemical instability.
Polyacrylonitrile (PAN) based gel electrolyte is a widely investigated system. Its structure swells and allows high solvent intake (˜80 wt %). High solvent intake is desirable as it leads to high ionic conductivity. The conductivity of PAN gel electrolyte was expected to be close to that of the corresponding liquid electrolyte, but it was found to be an order of magnitude less than the conductivity of the liquid electrolyte.